NAME¶
TIFFRGBAImageOK, TIFFRGBAImageBegin, TIFFRGBAImageGet, TIFFRGBAImageEnd - read
and decode an image into a raster
SYNOPSIS¶
#include <tiffio.h>
typedef unsigned char TIFFRGBValue; typedef struct _TIFFRGBAImage
TIFFRGBAImage;
int TIFFRGBAImageOK(TIFF *tif, char
emsg[1024])
int TIFFRGBAImageBegin(TIFFRGBAImage *img, TIFF*
tif, int stopOnError, char
emsg[1024])
int TIFFRGBAImageGet(TIFFRGBAImage *img, uint32*
raster, uint32 width , uint32
height)
void TIFFRGBAImageEnd(TIFFRGBAImage *img)
DESCRIPTION¶
The routines described here provide a high-level interface through which
TIFF images may be read into memory. Images may be strip- or
tile-based and have a variety of different characteristics: bits/sample,
samples/pixel, photometric, etc. Decoding state is encapsulated in a
TIFFRGBAImage structure making it possible to capture state for
multiple images and quickly switch between them. The target raster format can
be customized to a particular application's needs by installing custom
routines that manipulate image data according to application requirements.
The default usage for these routines is: check if an image can be processed
using
TIFFRGBAImageOK, construct a decoder state block using
TIFFRGBAImageBegin, read and decode an image into a target raster using
TIFFRGBAImageGet, and then release resources using
TIFFRGBAImageEnd.
TIFFRGBAImageGet can be called multiple times
to decode an image using different state parameters. If multiple images are to
be displayed and there is not enough space for each of the decoded rasters,
multiple state blocks can be managed and then calls can be made to
TIFFRGBAImageGet as needed to display an image.
The generated raster is assumed to be an array of
width times
height 32-bit entries, where
width must be less than or equal to
the width of the image (
height may be any non-zero size). If the raster
dimensions are smaller than the image, the image data is cropped to the raster
bounds. If the raster height is greater than that of the image, then the image
data are placed in the lower part of the raster. (Note that the raster is
assume to be organized such that the pixel at location (
x,
y) is
raster[
y*
width+
x]; with the raster origin in the
lower-left hand corner.)
Raster pixels are 8-bit packed red, green, blue, alpha samples. The macros
TIFFGetR,
TIFFGetG,
TIFFGetB, and
TIFFGetA should
be used to access individual samples. Images without Associated Alpha matting
information have a constant Alpha of 1.0 (255).
TIFFRGBAImageGet converts non-8-bit images by scaling sample values.
Palette, grayscale, bilevel,
CMYK, and YCbCr images are
converted to
RGB transparently. Raster pixels are returned
uncorrected by any colorimetry information present in the directory.
The parameter
stopOnError specifies how to act if an error is encountered
while reading the image. If
stopOnError is non-zero, then an error will
terminate the operation; otherwise
TIFFRGBAImageGet will continue
processing data until all the possible data in the image have been requested.
To use the core support for reading and processing
TIFF images,
but write the resulting raster data in a different format one need only
override the ``
put methods'' used to store raster data. These methods
are are defined in the
TIFFRGBAImage structure and initially setup by
TIFFRGBAImageBegin to point to routines that pack raster data in the
default
ABGR pixel format. Two different routines are used
according to the physical organization of the image data in the file:
PlanarConfiguration=1 (packed samples), and
PlanarConfiguration=2 (separated samples). Note that this mechanism can
be used to transform the data before storing it in the raster. For example one
can convert data to colormap indices for display on a colormap display.
SIMULTANEOUS RASTER STORE AND DISPLAY¶
It is simple to display an image as it is being read into memory by overriding
the put methods as described above for supporting alternate raster formats.
Simply keep a reference to the default put methods setup by
TIFFRGBAImageBegin and then invoke them before or after each display
operation. For example, the
tiffgt(1) utility uses the following put
method to update the display as the raster is being filled:
static void
putContigAndDraw(TIFFRGBAImage* img, uint32* raster,
uint32 x, uint32 y, uint32 w, uint32 h,
int32 fromskew, int32 toskew,
unsigned char* cp)
{
(*putContig)(img, raster, x, y, w, h, fromskew, toskew, cp);
if (x+w == width) {
w = width;
if (img->orientation == ORIENTATION_TOPLEFT)
lrectwrite(0, y-(h-1), w-1, y, raster-x-(h-1)*w);
else
lrectwrite(0, y, w-1, y+h-1, raster);
}
}
(the original routine provided by the library is saved in the variable
putContig.)
The
TIFFRGBAImage routines support the most commonly encountered flavors
of
TIFF. It is possible to extend this support by overriding
the ``
get method'' invoked by
TIFFRGBAImageGet to read
TIFF image data. Details of doing this are a bit involved, it
is best to make a copy of an existing get method and modify it to suit the
needs of an application.
NOTES¶
Samples must be either 1, 2, 4, 8, or 16 bits. Colorimetric samples/pixel must
be either 1, 3, or 4 (i.e.
SamplesPerPixel minus
ExtraSamples).
Palette image colormaps that appear to be incorrectly written as 8-bit values
are automatically scaled to 16-bits.
RETURN VALUES¶
All routines return 1 if the operation was successful. Otherwise, 0 is returned
if an error was encountered and
stopOnError is zero.
DIAGNOSTICS¶
All error messages are directed to the
TIFFError(3TIFF) routine.
Sorry, can not handle %d-bit pictures. The image had
BitsPerSample
other than 1, 2, 4, 8, or 16.
Sorry, can not handle %d-channel images. The image had
SamplesPerPixel other than 1, 3, or 4.
Missing needed "PhotometricInterpretation" tag. The image did
not have a tag that describes how to display the data.
No "PhotometricInterpretation" tag, assuming RGB. The image was
missing a tag that describes how to display it, but because it has 3 or 4
samples/pixel, it is assumed to be
RGB.
No "PhotometricInterpretation" tag, assuming min-is-black. The
image was missing a tag that describes how to display it, but because it has 1
sample/pixel, it is assumed to be a grayscale or bilevel image.
No space for photometric conversion table. There was insufficient memory
for a table used to convert image samples to 8-bit
RGB.
Missing required "Colormap" tag. A Palette image did not have a
required
Colormap tag.
No space for tile buffer. There was insufficient memory to allocate an
i/o buffer.
No space for strip buffer. There was insufficient memory to allocate an
i/o buffer.
Can not handle format. The image has a format (combination of
BitsPerSample,
SamplesPerPixel, and
PhotometricInterpretation) that can not be handled.
No space for B&W mapping table. There was insufficient memory to
allocate a table used to map grayscale data to
RGB.
No space for Palette mapping table. There was insufficient memory to
allocate a table used to map data to 8-bit
RGB.
SEE ALSO¶
TIFFOpen(3TIFF),
TIFFReadRGBAImage(3TIFF),
TIFFReadRGBAImageOriented(3TIFF),
TIFFReadRGBAStrip(3TIFF),
TIFFReadRGBATile(3TIFF),
libtiff(3TIFF)
Libtiff library home page:
http://www.remotesensing.org/libtiff/